In an airplane turbojet, for example, the afterbody extending radially inside the high pressure turbine and downstream therefrom can be provided with a stream-shaping element that is known as an exhaust cone, which element extends axially between the high pressure turbine and the post-combustion injectors. The element channels the annular stream internally as far as the injector arms for post-combustion. It is also arranged to combat unwanted vibration (known as “screech”) by having series of holes formed in its downstream portion.
As a general rule, that element is made of metal and at its downstream end it includes a circular opening having a kind of reentrant cover engaged therein, which cover is likewise made of metal. The assembly is advantageously arranged to contribute to attenuating the above-mentioned vibrations, and in particular to preventing resonance phenomena from forming.
In operation, such an exhaust cone is raised to high temperatures and it is subjected to a temperature gradient over its upstream portion. This gives rise to radial and axial expansions that are absorbed by the flexibility of the various assembled-together parts. The equilibrium point of these expansions leads to high levels of stress which, in combination with the high temperature, shorten the lifetime of the exhaust cone.
To increase its lifetime, attempts have been made in particular to fit an exhaust cone that is made out of composite material, and in particular out of CMC. That solution is advantageous, not only because it increases lifetime, but also because it obtains a reduction in weight. Nevertheless, since the coefficient of expansion of a CMC material is much less than that of a metal, that kind of assembly is difficult to implement.